This invention relates to a system and method of detecting the weight and position of an occupant of a motor vehicle for purposes of allowing or suppressing air bag deployment.
Vehicle occupant detection systems are useful in connection with air bags and other pyrotechnically deployed restraints as a means of judging whether, and how forcefully, to deploy the restraint. One fundamental parameter in this regard is the weight of the occupant, as weight may be used as a criterion to distinguish between an adult and an infant or small child.
One prior weight estimation technique is to install an array of variable resistance pressure sensitive elements in the seat, and to sum the individual pressures to determine occupant weight. A restraint system based on this technique is shown and described in the U.S. Pat. No. 5,474,327, issued on Dec. 12, 1995, and assigned to the assignee of the present invention. In practice, however, such systems tend to be relatively costly to implement, and require a significant amount of signal processing for proper calibration and weight estimation.
Another approach for determining occupant weight, disclosed for example in U.S. Pat. No. 5,987,370, issued on Nov. 16, 1999, and assigned to the assignee of the present invention, involves installing a fluid-filled polymeric bladder in or under the bottom cushion of a vehicle seat, and measuring the fluid pressure in the bladder. As disclosed in the U.S. Pat. No. 6,101,436, issued on Aug. 8, 2000, and also assigned to the assignee of the present invention, the bladder may have multiple cells formed by a pattern of spot welds between top and bottom layers of the bladder, creating an array of generally circular or hexagonal cells between which the fluid can freely flow. This approach can maximize the pressure response for improved sensitivity, and minimize the amount of fluid required to detect occupant weight, thereby minimizing the weight of the fluid-filled bladder. However, the position of the occupant on the seat can influence the indicated weight, and therefore, the decision as to whether to allow or suppress air bag deployment. Also, the decision as to whether to allow or suppress air bag deployment may depend on occupant position, as well as occupant weight. For example, if the occupant is very close to the point of deployment, it may be desired to disable deployment regardless of the occupant weight. For this reason, a number of position detection systems have been devised for independently determining if the occupant is out of position and in danger of injury due to air bag deployment. However, the use of multiple independent sensing systems significantly increases the system cost and complexity, and introduces a number of implementation issues, such as sensor placement and calibration. Accordingly, what is desired is a simple and cost-effective occupant detection system that takes into consideration both occupant weight and occupant position.
The present invention is directed to an improved occupant detection system involving a fluid-filled polymeric seat cushion bladder defining multiple fluid-filled chambers corresponding to different regions of the seat cushion, with no fluid flow between such chambers, and where the fluid pressures in the various individual chambers are detected and processed to develop a weight estimation that is compensated for occupant position. According to the invention, the chambers are configured to detect occupant weight in at least forward, rearward, inboard and outboard regions of the bottom seat cushion. When the detected pressures are unevenly distributed and the pressure in the forward, rearward, inboard or outboard regions of the seat exceeds the average pressure by at least a predetermined amount, a composite pressure indicative of occupant weight is adjusted in a direction to bias the suppression status in favor of allowing restraint deployment, unless the occupant is forwardly positioned on a seat that is also forwardly positioned.